304 CHAP. XXVII. ANAESTHETICS AND GEOTROPISM 



cases. The cut specimen was held in an inverted position, 

 and after the attainment of uniform up-movement, car- 

 bonic acid gas was apphed ; this caused a reversal of the 

 normal geotropic movement in the course of 4 minutes and 

 20 seconds ; the petiole was thus lowered below its original 

 position. Introduction of fresh air gave rise, in the course 



Fig. 180. 



Fig. 181, 



Fig. 180. Effect of CO2 on geotropic response of Mimosa, applied 

 at arrow ; second arrow within a circle represents substitu- 

 tion of fresh air. 



Successive dots at intervals of a minute. 



Fig. 181. Effect of COg on geotropic response of Erythrina indica. 

 Note actual reversal of geotropic response under COg. 



of 2 minutes, to the renewal of normal erectile movement 



(fig. 181). 



Results obtained with various growing and pulvinated 

 organs thus show that the normal geotropic response is 

 reversed under the continued action of carbonic acid gas. 

 The effect of CO2 in reversal of geotropic response is by 

 no means unique, for it occurs under the action of other 

 anaesthetics as well. The period of application of the 

 anaesthetic for reversal is relatively shorter in the case of 

 strong anaesthetic like chloroform, but the fundamental 

 reaction is similar in all cases. 



